1. Field of the Invention
The present invention relates to internal combustion engines, and more particularly to a multiple vane rotary internal combustion engine.
2. Background Art
A. Reciprocating Piston Engines
The internal combustion engine has been used in many applications since its introduction. Today, the most commercially successful version of the internal combustion engine utilizes pistons secured at one end to a crankshaft, rotation of which reciprocates the pistons within cylinders. While the reciprocating version of the internal combustion engine is fraught with disadvantages when compared to other versions of the internal combustion engine, years of research and development have been expended making the reciprocating piston engine more reliable and efficient.
The efficiency of any internal combustion engine depends on how completely the fuel is combusted within the engine. Combustion is accomplished using either a two-phase or four-phase combustion cycle. While recent advances have been made in two-phase engines, the vast majority of modern engines utilize the four-phase combustion cycle.
The events occurring during the four phase combustion cycle include:
1) Intake Phase
During the intake phase, a charge of an air and fuel mixture is drawn into a combustion chamber;
2) Compression Phase
The charge is compressed to a point of optimal volume; and ignited during the latter part of the Compression Phase of the cycle to initiate combustion of the fuel and air mixture and to cause an increase in the temperature and pressure of gases in the charge;
3) Power or Work Phase
The mechanical power is created by harnessing the work produced by the expanding gases of combustion to propel a piston or rotor; and
4) Exhaust Phase
Spent gases and products of combustion are exhausted from the combustion chambers.
The efficiency of the four-phase combustion cycle is influenced by many factors: (a) the temperature of the combustion chamber and relative temperature of the intake charge; (b) the compression ratio; (c) the efficiency of the ignition system; and (d) most of all by the speed of the engine as measured in revolutions per minute (RPM).
All reciprocating piston engines have an optimal speed of operation. While this speed may be maintained for long periods in industrial, commercial, or aircraft applications, most other applications require that the engine be operated at varying speeds.
At speeds below the optimal operating speed of the engine, combustion is inefficient, but no immediate detrimental effects are usually exhibited by the engine.
As the speed of reciprocating piston engines increases past the point of optimal efficiency, however, the air and fuel mixture may not totally combust during the recurring power phases and may actually continue to burn into the exhaust phase. This results in the familiar phenomenon commonly referred to as an exhaust "backfire." The continued expansion of burning gases in combination with unburned fuel in the exhaust phase may also cause less than optimal evacuation of the spent products of combustion.
When the intake phase is initiated following an ineffective exhaust phase, the remaining unburned gases in the combustion chamber left over from the previous exhaust phase may cause entering gases to be displaced, thereby causing a less than optimal charge from being drawn into the combustion chamber. This less than optimal incoming charge may even ignite prematurely during the intake and compression phases of combustion due to the residual products of combustion.
If the incoming charge is ignited in the intake phase, the charge will undergo combustion resulting in an intake backfire through the intake port and induction system. If the incoming charge ignites during the compression phase of combustion, the premature ignition causes expansion of the gases in the combustion chamber. The mechanical energy required to compress expanding gases is naturally greater than the energy required to compress gases at atmospheric pressure. The resultant increase in needed energy to compress the air and fuel mixture introduces drag on the engine which reduces efficiency and may actually halt the rotation of the engine.
The inefficient combustion of the air and fuel mixture at high engine speeds may also be exacerbated by the ignition system. At high engine speeds, the number of sparks per minute that are needed to ignite the charges in the combustion chambers often tax the ignition system to the point where the spark becomes weak.
When the engine speed exceeds the ability of the ignition system to deliver a spark of suitable strength, complete combustion of the charge is delayed until late in the work phase and may not occur before the charge is evacuated during the exhaust phase. This results in both the presence of unburned fuel in the exhaust system, causing backfires, and in the presence of rapidly expanding partially burned and burning fuel remaining in the combustion chamber. The incoming charge of air and fuel is met by the expanding gases remaining in the combustion chambers resulting in less charge being taken into the combustion chamber than a totally evacuated combustion chamber thereby decreasing the efficiency of the engine.
To improve the strength of the spark provided to the air and fuel charge in the combustion chamber, complex multiple discharge and multiple-coiled ignition systems have been developed. These systems benefit the combustion cycle by providing a stronger spark to each combustion chamber. An advantage of multiple spark systems is that combustion is initiated simultaneously at several points within the combustion chamber. This increases both the speed and the thoroughness of combustion.
While these complex ignition systems often substantially improve the efficiency of the spark provided at high engine speeds, the complexity of these ignition systems often results in unreliability and frequent maintenance. Their presence also limits the space available for intake and exhaust valves, thereby decreasing the efficiency of the intake or exhaust phases of the combustion cycle.
Ignition systems work in conjunction with compression ratios to limit the types of fuel and the range of fuel and air mixtures that may be combusted in an engine. For example, engines which burn less volatile fuels, such as diesel fuel utilize a compression ratio so high as to require no spark. Ignition is accomplished through the introduction of fuel in an atomized stream into the highly compressed, hot air. The flame spreads across the charge in the combustion chamber, requiring more time to combust than with more volatile fuels, such as gasoline, but nevertheless producing a more smooth explosion with less shock to the engine.
Likewise, fuels that are more volatile than gasoline such as hydrogen must utilize a relatively low compression ratio or risk premature ignition when the charge is compressed to the same volumes as gasoline-based charges. For this reason, more ecologically desirable fuels with high volatilities cannot be burned in gasoline-based reciprocating piston engines without incurring the risk of damage to the engine. Considerable modification of the compression ratios and induction systems of gasoline-based engines is usually required before fuels such as hydrogen can be burned reliably.
Reciprocating piston engines are susceptible to damage from the use of more volatile fuels because of the reciprocating nature of the engine. The force produced by combustion of very volatile fuels tends to push the piston out the bottom of the engine before the crankshaft can reverse the direction of travel of the piston. This reversal process is the cause of much of the shock and vibration associated with reciprocating piston engines. Repeated exposure to these shocks can substantially decrease the life of the engine.
Reciprocating piston engines must reverse the direction of the piston upon completion of each phase of the combustion cycle. This reversal imposes a limit on the maximum engine speed attainable. To enable sufficient speed for an engine to be usable, the weight of the reciprocating mass of the piston and connecting rod must be kept low. At the same time the strength of the connecting rod between the reciprocating pistons and the crankshaft must be sufficient to overcome the shock and vibration of constant reciprocation of the piston within the cylinder. These shocks are compounded in reciprocating piston engines by the number of pistons, the speed of the engine, and the orientation of the cylinders within the engine. Many of the advances in reciprocating piston engines have centered on overcoming these inherent vibration problems by attempting to balance the vibrations with counter-balance shafts and by reorienting the cylinders into different configurations.
B. Wankel Rotary Engines
In an attempt to devise an internal combustion engine that does not exhibit the static and dynamic balancing problems associated with reciprocating piston engines, rotary engines have been developed. Rotary engines generally exhibit an increased power-to-weight ratio due to a reduction of friction and an increase in efficiency derived from the rotary action of the engine.
The Wankel engine is one type of a rotary engine. A Wankel engine has a generally triangularly shaped trochoidal rotor and a rotor chamber housing having its inner wall configured to conform to the oscillations of the trochoidal rotor. The rotor housing is configured to place the three lobes of the rotor in constant engagement with the inner wall of the rotor chamber housing This constant engagement causes relatively rapid wear on the lobes and housing. Many of the recent advances in the Wankel engine focus on the improvement of the seals between the rotor lobes and the inner wall of the rotor housing.
The intake and exhaust valves and the sparkplug need to be centrally located in the combustion chamber of all internal combustion engines for optimal efficiency. Compromises in either intake and exhaust valve placement or in sparkplug location must be accepted, however, because of space constraints within the cylinders of reciprocating piston engines. These compromises have led to less than optimal combustion taking place in most reciprocating engines. Because of these inherent weaknesses, much of the research and development occurring on behalf of reciprocating engines has been directed at these problems. The recent influx of multiple valve engines and dual sparkplug cylinder heads on the market bears record of the results of this research. Even multiple valve engines, however, do not totally overcome the problems associated with the arrangement of the valves and sparkplug within the combustion chamber of reciprocating piston engines.
Rotary engines, however, do not share the same inherent weaknesses in combustion chamber design. Most rotary engines in effect rotate each combustion chamber past the intake port prior to ignition. This results in the freedom to locate the intake port at the optimal location for combustion chamber filling, without regard to interference from the exhaust valve or ignition system. Thereafter, each combustion chamber is rotated past the sparkplug, which can similarly be optimally located. The rotary arrangement thereby avoids the need to have an intake or exhaust valve physically enter the combustion chamber and therefore, dispenses with complicated valve train components and their inherent unreliability and complexity.
Other advantages of rotary engines over reciprocating piston engines include the following: more convenient internal cooling of the rotor; higher compression ratios permissible without engine knocking owing to combustion chamber arrangement; a low size-to-power output ratio; fewer moving parts; and operation with decreased noise and vibration.
Despite the aforementioned advantages of rotary engines, the reciprocating engine continues to enjoy widespread use in the automotive industry because it provides high pressure sealing by the simple and reliable usage of sprung rings obstructing the blow-by of gases between the piston and cylinder wall.
In a Wankel type rotary engine, such sprung rings are replaced by seals between the epitrochoidal rotor and the housing. Because the rotor lobe apex is in constant contact with the inner wall of the housing, an apex seal must retain a sealing interface throughout the rotor's epitrochoidal revolutions The working face of this apex seal must tolerate thrusts over a wide range of angles relative to the inner wall as its approach to the work varies from thrust to drag two times for each revolution of the rotor. The need to maintain constant contact limits the inherent dynamic balance available to rotary engines because of the high specific bearing pressure exerted by the apex seal on the inner wall of the housing.
A reciprocating piston engine utilizes only the upper surface of the cylindrical piston to produce work. In contrast to a reciprocating piston engine with only one working surface, the three outside faces of an epitrochoidal rotor provide extensive operating surfaces which are constantly deployed in useful processes. In the reciprocating internal combustion engine using a four-phase combustion cycle, the crankshaft must revolve two times to recover the beginning attitude in preparation for another cycle. This produces one power stroke per two revolutions of the crankshaft. Epitrochoidal rotary engines, however, obtain one power stroke per revolution.
Epitrochoidal Wankel engines utilize the same four phase combustion cycle discussed above. Because of the higher speeds attainable with engines that do not reciprocate, there is a higher probability that rotary engines will operate at speeds greater than the optimal speed for combustion of the charge within the combustion chamber. Although the more efficient placement of intake and exhaust ports and sparkplugs increases the efficiency of the rotary engine, the reduction in friction elevates the maximum engine speed beyond the capacities of even the improved ignition and induction systems.
C. Vaned Rotary Engines
Another type of rotary engine designed to overcome the disadvantages of reciprocating piston engines is the vaned rotary engine. Rather than using a trochoidal rotor, the typical vaned rotary engine utilizes a circular rotor carried eccentrically within a fixed housing which defines a rotor chamber. The periphery of the rotor is usually divided by radially extensible and retractable vanes. Each combustion chamber is defined between a pair of successive vanes, a portion of the rotor therebetween, and the rotor housing enclosing the chamber. As the combustion chamber revolves around the inside of the housing, the plural combustion chambers continuously change in volume due to the eccentric rotation of the rotor.
The phases of the combustion cycle are accomplished by positioning the intake and exhaust ports at advantageous locations within the rotor housing,. As the combustion chamber expands and contracts, the changing volume serves to drawn in and expel gases.
The radially spaced movable vanes are arranged in increments about the periphery of the rotor. The tips of these vanes typically must form a tight seal with the inner wall of the rotor housing to sealingly divide the rotating combustion chambers from each other. This separation prevents the various phases of the combustion process from overlapping and interfering with subsequent phases.
As with Wankel engines, however, rapid wear of the seals occurs between the vane tips and the inner wall of the rotor housing.
As the speed of a vane-type rotary engine increases, the vanes tend to elongate and contact the inner surface of the housing with greater pressure. This elongation expedites wear on the housing and precipitates early degradation of the housing.
A further problem associated with both reciprocating and rotary engines occurs because of the dependency of these engines on a lubricant pump to pressurize and circulate lubricant to the friction surfaces of the engine. A malfunction in the lubricant pump precipitates rapid engine degradation leading to eventual destruction of the engine. As a result, the useful life of the engine depends on the proper functioning of the lubricant pump.
It would, therefore, be an advancement in the art to provide an internal combustion engine that is free from reliance on a lubricant pump to pressurize and circulate lubricant throughout the engine.
Another advancement in the art would be to provide an internal combustion rotary engine that does not wear rapidly at the point of interface between the rotor or vanes and the inner wall of the rotor housing.
Still another advancement in the art would be to provide an internal combustion engine that is capable of using a variety of fuels having volatilities greater than gasoline, while retaining the ability to operate when fueled by gasoline.
Yet another advancement in the art would be to provide an internal combustion engine that becomes more efficient at high engine speeds. A further advancement in the art would be to provide an internal combustion engine that does not suffer from incomplete exhaust scavenging during high engine speeds.
A still further advancement in the art would be to provide an internal combustion engine that has a simplified and reliable ignition system.
Another advancement in the art would be to provide an internal combustion engine that does not suffer from a weak spark during high engine speeds.
Yet another advancement in the art would be to provide an internal combustion engine that is free of the vibrations incurred from reciprocating pistons.
Still another advancement in the art would be to provide an internal combustion engine that is free of the imbalances and stresses imposed by reciprocating pistons.